Sandblasting installation

ABSTRACT

A SAND AND AIR MIXING CHAMBER IN A SANDBLASTING INSTALLATION HAS A SAND FEED TUBE EXTENDING THEREINTO FROM ABOVE AND A BOTTOM PORTION, WHICH IS VERTICALLY ADJUSTABLE TOWARDS AND AWAY FROM THE LOWER OUTLET END OF SAID FEED TUBE.

Nov. 9, 1971 P, WEIJSENBURG 3,613,253

SANDBLASTING INSTALLATION Filed Jan. 28, 1969 IN V EN TOR.

R r Irsien My Patented Nov. 9, 1971 3,618,263 SANDBLASTING INSTALLATION Per Torsten Weijsenburg, Solna, Sweden, assignor to Atlas Copco Aktiebolag, Nacka, Sweden Filed Jan. 28, 1969, Ser. No. 794,522 Int. Cl. B24c 3/04 US. Cl. 51-8 8 Claims ABSTRACT OF THE DISCLOSURE A sand and air mixing chamber in a sandblasting installation has a sand feed tube extending thereinto from above and a bottom portion, which is vertically adjustable towards and away from the lower outlet end of said feed tube.

This invention relates to sandblasting installations and more specifically the invention is concerned with the mixing chamber of such installations, where the sand is mixed with a gaseous transporting medium under pressure, commonly air, before arriving to the sandblasting nozzle.

Previously known sandblasting installations suffer from certain drawbacks which make them less useful for many cleaning and engraving tasks. Thus it is rather diflicult to accurately adjust the proportions of sand and air leaving the blasting nozzle during operation of the sandblasting equipment, and this is particularly the case, when frequent interruptions in the outflow of sand and air are required to properly perform the sandblasting work. Although means for adjusting the proportions of sand and air to be mixed have been provided also in certain prior sandblasting installations, these known means have been found rather unsatisfactory in practice, either because they were complicated in structure and unreliable in service, or because they comprise shutter means movable in direct contact with the sand so that they are very difficult to actuate.

It is the main object of this invention to provide an improved mixing chamber for a sandblasting installation which comprises simple and reliable means for accurate adjustment of the proportions of sand and air to be mixed.

It is another object of the invention to provide an improved mixing chamber of the kind referred to, wherein the proportions of sand and air can be easily and accurately adjusted also during actual operation of the sandblasting installation and in a manner always assuring the best possible distribution of the sand in the passing air, and wherein the entrance of sand is automatically restricted, when the flow of air therethrough is reduced or interrupted, so that undue accumulation of sand and hence clogging of the air passage in the mixing chamber can be avoided.

A further object of the invention is to provide a sandblasting installation comprising a sand and air mixing chamber, the walls of which are highly resistant to the abrasive wear of the airborne sand, and the cross section of which can be selectively changed by external actuating means in order to effect both adjustment of the outflow of sand from a sand container and simultaneous adaptation of the air passage within that area, where the passing air has to take up the sand.

These and other objects of the invention, which will become apparent as this description proceeds, are achieved with a sandblasting installation comprising a sand container, a mixing chamber located therebeneath and forming part of a conduit extending from a source of gaseous sand transporting medium under pressure to a blasting nozzle, and a sand feed tube connecting the sand container with the mixing chamber and having a lower end portion extending from above into the mixing chamber in a manner to leave a free flow passage for the gaseous medium through the upper portion thereof, and which is characterized in that the mixing chamber has a bottom portion under the sand feed tube, which is vertically adjustable towards and away from the lower end of the sand feed tube.

Further features of the invention will become apparent from the following detailed description of a preferred embodiment of the invention, which has been illustrated somewhat diagrammatically in the accompanying drawing, wherein FIG. 1 is a longitudinal sectional elevation of the lower portion of a sand container and a mixing chamber there beneath, the upper part of the container being indicated by dash-and-dot lines,

FIG. 1A is a longitudinal sectional elevation of a sandblasting nozzle connected to the outlet end of the mixing chamber shown in FIG. 1, and

FIG. 2 is a partial end view showing the interior of the mixing chamber in FIG. 1.

In the drawing numeral 1 designates a pressure-tight sand container having at its top a removable lid 1' covering an opening, through which sand can be filled into the container, when required. By means of a flanged bracket 2 the lower end of the container 1 is secured to the upper side of a horizontally extending, tubular casing 3 having an internal lining 4 of elastic material, such as rubber or the like. The interior of the lined casing 3 represents the mixing chamber 5 of the installation and forms part of a conduit, through which a gaseous sand transporting medium under pressure, commonly air, can be passed, as will more clearly appear from the following.

The sand from the container 1 enters the mixing chamber 5 through a feed tube 6, which is threaded through a hole in the bracket 2 and the axial position of which may be vertically adjusted by screwing the tube in or out. The feed tube 6 has a lower end portion, which penetrates the lining 4 and extends from above a certain distance into the mixing chamber 5. At the lower end of the feed tube 6 there is an outlet opening 7 for the sand, and under this opening the sand will normally form a small, substantially conical heap 8 on the bottom portion of the mixing chamber beneath the feed tube 6, at least when there is substantially no flow of air through the mixing chamber. As shown in FIG. 2, the feed tube 6 is narrow enough to leave a substantial upper part of the cross sectional area of the mixing chamber 5 free for the passage of air, and the heap 8 of sand can never grow so large that it blocks the passage through the mixing chamber.

The one or left hand end of the mixing chamber 5 is through a conduit 9, indicated by dash-and-dot lines, and a main valve 10 connected to a source of air under pressure, such as a compressor unit, not shown. A branch conduit 11 supplies pressure to the sand container 1 in the usual manner, when the valve 10 is open. The valve 10 is, preferably, a three-way valve capable of removing the pressure from the mixing chamber 5 and the sand container 1 by connecting them to the atmosphere, when the supply of pressurized air from the compressor unit is shut off.

The other or right hand end of the mixing chamber 5 is through a suitable hose conduit, indicated by the dash-and-dot line 12, connected to a pistol-like blasting nozzle, which has been generally designated by numeral 13. This blasting nozzle is provided with a shut-off mechanism permitting instantaneous interruption of the sandblast and comprising, in the example as shown, an arm 14 connected to a manually actuatable trigger 15 and urged by a spring 16. The spring 16 tends to move the outer end of the arm 14, where a small plate 17 of wear resistant material, such as tungsten carbide, is attached, upwardly towards and against the outlet opening of the blasting nozzle 18 proper, so that the blast is shut off. When the trigger 15 is manually actuated, and the main valve 10 is open, the air from the compressor unit will start flowing through the mixing chamber 5, become mixed with sand therein and pass out through the nozzle 18 together with the suspended sand. The heap 8, from which the sand grains are removed by the passing air, is continuously replenished from the sand container 1 by free gravity outflow of sand therefrom through the feed tube 6. If required, the outflow of sand from the container 1 may be promoted by vibration in a manner well known per se.

To the lower side of the casing 3 there is secured a vertical sleeve member 19 forming a housing or cylinder for a vertically movable piston 20. The position of this piston 20, which in fact forms a pusher member, may be adjusted by a set screw 21, which is threaded in through a lid or closure 22 forming the bottom of the sleeve member 19. The piston 20 suitably has a rounded or bevelled upper edge and acts against the lower side of that section of the elastic lining 4, which forms the bottom of the mixing chamber and more specifically the portion of said bottom lying directly below the outlet opening 7 of the sand feed tube 6.

By vertically adjusting the piston 20, the bottom portion of the lining 4 may be elevated or lowered accordingly and hence moved towards or away from the outlet opening 7 of the sand feed tube 6. As will be readily understood, this will cause a variation in the size of the sand heap 8 and, hence, in the proportions of sand and air being mixed. Since the lining 4 tends to elastically resist the upward movement of the piston 20, the latter needs actuation in the upward direction only. The movements of the piston 20, of course, causes a deformation of the lining 4 within the casing 3, whereby the cross sectional flow area of the mixing chamber will also be changed in a manner, which has been found very advantageous. Since the lining 4 is rather thick, the variation of the flow passage longitudinally through the mixing chamber 5 will always be smooth, which reduces the formation of undesirable turbulence within the mixing chamber.

In its uppermost position the piston 20 will cause the 0 inside of the lining 4 to contact the lower end of the sand feed tube 6 and to substantially close the sand outlet opening 7 therein. This is advantageous, because with the piston in that position the equipment may also be used as an air blower, and no harm can be caused, if the trigger of the blasting nozzle is unintentionally actuated. If desired, the piston 20 may be pneumatically or hydraulically actuated to close the sand outlet opening. The actuating fluid is supplied to the cylinder sleeve member 19 through a suitable conduit 23, and the piston is provided with seal 24 in the cylinder. The set screw 21 may be maintained also in such a case for defining the maximum outflow of sand.

It should be understood that although the mixing chamber may be used without the elastic lining 4, or with only a partial lining, such a lining has been found very advantageous since it is highly resistant to the abrasive wear of the airborne sand and will make the equipment durable and reliable in use. The lining also prevents the sand from interfering with the operation of the piston 20 and the set screw 21 representing the adjustment means. Consequently a smooth and accurate adjustment is assured. Of course, the said bottom section must be sufliciently large to carry the heap of sand formed under the feed tube. By proper pre-adjustment of the axial position of the feed tube, the deformation of the lining, when the piston is in its uppermost position, may be controlled so that the best possible mixing conditions are always prevailing.

I claim:

1. In a sandblasting installation the combination of a sand container; a mixing chamber located below said container and forming part of a conduit extending from a source of gaseous sand transporting medium under pressure to a blasting nozzle; a sand feed tube connecting said container with said mixing chamber and having a lower end portion extending from above into said mixing chamber to leave a free flow passage for the gaseous medium transversely past said end portion, said sand feed tube having a sand outlet opening in its lower end; a vertically adjustable bottom portion in said mixing chamber extending substantially horizontally and disposed below said sand feed tube forming a sand heap supporting area for collecting a conical sand heap thereon beneath said feed tube due to gravitation of sand from said container, the sand supporting area on said bottom portion exceeding the base width of said sand heap in any adjusted position of said bottom portion; and means for adjusting the vertical position of said bottom portion relative to the outlet end of said sand feed tube to adjust the size of the sand heap formed on the sand heap supporting area, thereby controlling the amount of sand surface subject to entrainment by said gaseous medium.

2. A sandblasting installation according to claim 1, wherein said adjustable bottom portion of the mixing chamber is elevatable into a position, in which it substantially closes the outlet of said sand feed tube.

3. A sandblasting installation according to claim 1, wherein said mixing chamber has an elastic lining, a bottom portion of which is adjustable towards and away from the lower outlet end of the sand feed tube, and wherein said means for adjusting the bottom portion of said mixing chamber comprises a pusher member arranged externally of said lining under the bottom portion thereof and actuatable against said elastic lining by an adjustable setting means.

4. A sandblasting installation according to claim 3, wherein said pusher member is actuatable by means of a set screw.

5. A sandblasting installation according to claim 3, wherein said pusher member is in the form of a pressure actuated piston.

6. A sandblasting installation according to claim 1, wherein the axial position of said sand feed tube is vertically adjustable relative to said vertically adjustable bottom portion of the mixing chamber.

7. In a blasting installation for an abrasive in granular form the combination of: an abrasive container; a housing below said container; a tubular mixing chamber in said housing; conduit branches extending respectively from a source of gaseous abrasive transporting medium under pressure to one end of said chamber and from the other end of said chamber to a blasting nozzle; a resilient liner in said chamber; an abrasive feed tube connecting said container with said mixing chamber and having a lower end portion extending from above through said liner centrally into said mixing chamber; an abrasive outlet opening at the lower end of said feed tube, said liner providing a bottom portion in said mixing chamber under and in spaced relation to said sand feed tube for collecting a conical heap of abrasive on said liner bottom portion beneath said opening for purposes of terminating the outflow due to gravitation of abrasive therethrough from said container; and means for adjusting the vertical position of said liner bottom portion relative to the outlet end of said sand feed tube thereby to adjust the size of. said heap of abrasive formed on said liner bottom portion actuatable by said transporting me dium, said adjusting means comprising a piston arranged vertically movably in said housing in alignment with said 5 feed tube externally of and in contact with said lining,

1,923,329 and means in said housing for setting said piston verti- 3 075 318 cally relative to said feed tube. 3199844 '8. An abrasive blasting installation according to claim 7, wherein said setting means is a set screw connected 5 to said housing and engageable with said piston.

References Cited UNITED STATES PATENTS 6 8/1933 Ruemelin 51-12 1/1963 Dilliard et a1 51-12 X 8/1965 Moore et al. 51-12 X FOREIGN PATENTS 7/1932 Australia 5112 LESTER M. SWINGLE, Primary Examiner 

